1. Field of the Invention
The present invention pertains to methods and apparatus for detecting malfunctions in electrical circuitry. More particularly, the present invention relates to methods and apparatus for detecting the loss in fidelity of signal reproduction as well as the loss in signal strength by an electrical circuit designed to process and reproduce electrical signals. Malfunctions of a circuit to be tested may be detected by the present invention whether such malfunctions are due to defects in the circuit to be tested proper, or due to loss of power caused by insufficient voltage provided by the pertinent power supply. Particular applications of the present invention are found in the detection of malfunctions in hearing aids.
2. Description of Prior Art
Various techniques for detecting malfunctions in electrical systems are well known. Traditional trouble-shooting techniques include removing a circuit to be tested from its normal functioning environment, and utilizing one or more signal-measuring devices while applying a test signal to various points in the circuit to be tested. Such trouble-shooting techniques, however, require that the circuit to be tested be unavailable for its intended functional purpose during the testing period. An alternate approach is to provide testing apparatus coupled to the circuitry to be tested on a permanent basis, thereby allowing specific parameters of the tested circuit to be monitored at all times. Such continuous monitoring may be significantly costly due to excessive power consumption by the test apparatus, and, where numerous parameters are being monitored, the test equipment may add considerable bulk to the original circuitry which is being monitored.
Particular testing problems arise in the field of hearing aids. Desirable features of modern hearing aids include compactness and light weight. Consequently, the addition of multiple-parameter, constant-monitoring test apparatus to a hearing aid may cause the entire unit to exceed critical bounds of both size and weight. A program whereby a hearing aid is periodically removed from service and tested for malfunctions is unsatisfactory, particularly in view of the fact that a replacement for the hearing aid being tested is required for the benefit of the user needing hearing assistance. Furthermore, since the user in need of a hearing aid may well depend upon such hearing assistance to function normally in society, the loss of use of a hearing aid due to a hearing aid malfunction between periodic testing times can result in the unavailability of such hearing assistance at unpredictable times, and for indeterminate periods.
An additional, and critical, factor involving the need to test hearing aids occurs when the user is a child, or is, for some other reason, relatively unsophisticated in the use of a hearing aid. In such case, a hearing aid malfunction may be present, and affecting the use of the hearing aid, without the detection of such malfunction by the user. For example, the strength of the signal produced by the hearing aid may be so poor that the user does not hear a significant portion of the signal picked up by the microphone of the hearing aid. Similarly, the tones from the ear piece of the hearing aid may not be true compared to the tones detected by the microphone due to frequency distortion in the reproduction of the signal by the amplifier of the hearing aid. In either case, a child using the hearing aid may not realize that there are deficiencies in the reproduction of the signal by the hearing aid. Continued use of the hearing aid under such circumstances may significantly impair the user's ability to function in a normal manner.